How to better realise the potential of automatic dishwashing to reduce the energy (and water) use in European households: introduction of a ‘short eco’ programme

1 Background

The “Sinner’s Circle” was first described by Herbert Sinner in a seminal early study on household washing machines and their potential to simplify domestic laundering. ¹ He identified how four factors – time, temperature, mechanics, and chemistry – impact the cleaning process by interacting and complementing each other. These factors are often depicted as sectors of a circle which, when complete, symbolises that the cleaning process has led to satisfactory results, i.e., that the laundry or any other item is clean. Sometimes, water is added to describe its connecting role as the solvent used. Sinner noted that “the size of the individual sectors can be quite different, meaning that the influence of one can be exchanged for the other to some extent.” ¹ Since its invention, the Sinner Circle has served as an effective visual tool (Figure 1A) for illustrating the complex interactions among these factors in various cleaning processes, including laundering and dishwashing.

Figure 1:

Combination of factors in a dishwashing process for an ‘eco’ programme (B) compared to a standard programme (A). To save energy, the cleaning temperature is decreased, and in turn, the cycle time is increased to achieve the same cleaning result according to Sinner’s circle (source: modified according to 1]).

Recently, Gonzalez-Torres et al. published a review highlighting the progress made over the past 40 years in European product policies. This includes initiatives such as Energy Labelling, Minimum Energy Performance Standards (MEPS), the Ecodesign Directive and voluntary agreements like the EU Ecolabel and Green Public Procurement. ² The authors conclude that the EU has focused heavily on efficiency in its energy policy as part of its strategy to mitigate climate change. Improving product efficiency is essential because it offers significant potential for energy savings; indeed, these products represent almost three-quarters of the primary energy supply.

In fact, EU initiatives related to energy labelling and ecodesign resulted in a 9 % reduction in energy consumption by 2020, and they are expected to further decrease energy use by 17 % by 2030, compared to a business-as-usual scenario. ² However, it has been suggested ³ that energy efficiency improvements may not be sufficient to reach the necessary targets defined in the United Nations’ Sustainable Development Goals (SDGs), established in 2015.

In this regard, dishwashing serves as a pertinent example to illustrate this assumption. The entire process of cleaning dishes can be done manually, as is common in developing countries where automatic dishwasher have not yet made a significant impact. ⁴ Observational studies conducted in both laboratories and households have clearly shown that manual dishwashing consumers on average much more water and energy than using an automatic dishwasher. ^{5 , 6 , 7 , 8 , 9}

Even in cases where an automatic dishwasher is available – estimated to be true for about 44 % of European households ¹⁰ – these machines are not used for washing all dish items. 20–40 % of dishes are still cleaned manually. ¹¹ Moreover, Richter ¹¹ noted that pre-rinsing dishes before loading a dishwasher must also be taken into account. In the past, this practice varied widely between countries. For instance, it was as low as 4 % in Germany but as high as 42 %, in Italy, resulting in an additional water consumption of 2.8 L and 19.7 L per dishwashing cycle, respectively.

Despite the optimization of dishwashers over the past few decades due to political regulations related to ecodesign and energy labelling, consumers still have a wide range of available programmes at their disposal. The ‘eco’ programme, which “is suitable for cleaning normally soiled tableware”, is defined as “the most efficient programme in terms of its combined energy and water consumption” – following the requirements of the ecodesign regulation EU 2019/2022. ¹² Yet, although this programme is intended for use in most dishwashing scenarios, research shows that consumers only use it for about (20–30) % of the cycles they start. ^{13 , 14} This discrepancy warrants further analysis.

These ‘eco’ programmes make use of the flexibility of programme design in a dishwasher, thus exploiting the “Sinner’s Circle” (Figure 1B). To achieve low energy use, the temperature of the programme must be reduced, because most of the energy needed is used to heat the water and the dishes during both the cleaning and the drying processes. Since the ‘chemical’ factor is fixed by the measurement standard (reference detergent type D, based on EN 60436) and the ‘mechanical’ factor largely determined by the hydraulic system of the dishwasher, only the ‘time’ factor remains to fulfil Sinner’s postulate that the circle must be filled in order to achieve good cleaning performance. This results in ‘eco’ programmes with long durations to allow the chemistry and the machine to compensate for a loss of performance from the ‘temperature’ factor (Figure 1B).

Despite the effectiveness of this technical principle, consumer research has shown that many consumers do not accept long cleaning programmes for various reasons. ¹⁵ One primary reason is that the percentage of people who understand that long cycles can be energy-efficient is smaller than the percentage of those who do not believe this. However, there are other reasons, related to the challenges in managing household chores. For instance, in daily life, dishes are not all ‘normally’ soiled; a wide range of soiling levels exist. Consequently, dishwasher manuals typically refer to these levels when recommending specific programmes. These soiling levels are characterised by verbal descriptions commonly used by detergent and dishwasher manufacturers, but also by consumer organisations, like Stiftung Warentest. The categories include:

1. Lightly soiled (e.g., breadcrumbs)

2. Normally soiled (e.g., sauce residues, teacups)

3. Heavily/highly soiled (e.g., grease/baked-on stains)

It should be noted that most dishwashers offer multiple programmes for each soiling level. For example, for ‘normally’ soiled dishes, programmes such as ‘auto’, ‘normal’, ‘powerwash’, ‘daily’, ‘universal’ and others may be available and recommended. Most of these programmes consume more energy and water than the ‘eco’ programme mandated by the ecodesign regulation. ^{15 , 16}

2 Complementary approaches

Given this framework, potential strategies to reduce energy use in home dishwashers – without requiring improvements to the dishwashing machines themselves – can focus on consumer behaviour. Recently, two groups have published several studies addressing this issue. Interestingly, this resulted in different conclusions and suggestions:

1st group: This group first conducted two online consumer surveys. One survey included participants from the UK, France, and Belgium and asked about the age of the dishwashing machine, the frequency of use, the pre-treatment undertaken before loading items into the dishwasher and the duration the dishes remained in the dishwasher. ¹⁷ The other survey was conducted in 11 European countries (including Israel) and asked consumers about the model type of their dishwasher, the available cycles, and the most commonly used cycles. Additionally, consumption data, programme durations and the maximum temperatures reached within these programmes were collected from manuals of 164 dishwasher models from 31 best-selling manufacturers, representing the installed base of the European market. These programme data were sorted according to seven generically defined programmes, and averages of consumption data, programme durations, and maximum temperatures were calculated.

Considering that ‘eco’ programmes are often not well accepted due to their long duration, this study suggested that Short programmes, which on average last about 30 min and consume little energy and water, might be an economical and convenient alternative to the more time-consuming ‘eco’ programmes. In fact, some short programmes were found to consume less energy for a full load (0.74 kWh on average) than the average ‘eco’ programmes (0.90 kWh). However, as noted by the authors, these short programmes are primarily designed for cleaning lightly soiled dishes.

Since cleaning performance is the most important factor for the acceptance of a programme and might not be as effective for ‘normally’ soiled dishes in short programmes as in ‘eco’ programmes, the group conducted another study to investigate the cleaning performance of different dishwasher programmes on various soils using four different market detergents. The results clearly show that the choice of detergent has a major influence on the cleaning results, especially for short cycles and that, specific short cycle and detergent combinations achieved results nearly as effective as those from ‘eco’ cycles. ¹⁸ Consequently, it was concluded that some short cycles are suitable for tackling more than lightly soiled dishes and might even be suitable for everyday use when paired with high-performing cleaning products.

Finally, this group showed through modelling with a freely programmable dishwasher that certain short programme combinations can clean normally soiled dishes in less than 55 min – typically 30 min – while using significantly less energy than average ‘eco’ programmes using a commercially available detergent. ¹⁹

2nd group: This group surveyed consumer claimed behaviour regarding dishwasher use in a representative sample of the population from eight major European countries. ^{20 , 21} From this data, a model was generated to calculate the average consumption values per programme for each country, along with a model of the consumption values for the installed base of dishwashers in each country across seven generic programmes. In this study group, the use of ‘modifiers’ (i.e., special functions that can be deliberately selected by the consumer on the dishwasher) and the degree of soiling on the dishes for each programme used were also surveyed. As a result, a considerable separation in programme selection related to the degree of soiling on the dishes could be determined for all countries.

Within each soiling level (i.e., lightly, normally, and heavily soiled), the consumption model was used to identify a programme that requires the least amount of energy. ¹⁶ For lightly soiled dishes the most efficient option is the ‘short/low temperature’ (∼30 min) programme. For normally soiled items, the ‘eco’ programme is the best choice, while heavily soiled dishes require the intensive programme. In addition, using a modifier to shorten the programme duration was found to increase the resource use considerably. Considering these findings, the authors concluded that the ‘eco’ programme might serve as a replacement for all programmes that are intended (and are being used) for normally soiled dish items, like the normal, auto, and quick/high temperature (called 65°, power, plus, etc.) programmes. By following this approach, the consumer must accept the longer programme duration as this provides good cleaning while using fewer resources (energy and water). For lightly soiled dishes, the quick/low temperature (called 45°, Jet, 30′, Express, etc.) programme was deemed to be suitable.

Finally, the use of modifiers was identified as increasing the energy consumption inadequately. The second group concluded that following their recommendations could save up to 22.5 % of energy and 18 % of water without compromising on cleaning performance.

3 Critical review of the studies

Considering the insights from the studies mentioned above, it is clear that both groups approached the topic from different perspectives, which is an important point for discussion.

First, the approach used by the first group cannot be directly applied to recommendations for manufacturers and consumers. This is because the term ‘short’ can refer to a wide variety of programmes that differ between dishwashers, making it difficult to clearly match these programs to those available on the market. Second, drying performance was excluded in order to focus on cleaning performance. And third, cleaning performance was evaluated using the IKW method, which does not allow for comparison with results obtained according to the IEC standard 60436, for example, because other stains and loading schemes are used by the two methods and the performance evaluations is done differently.

On the other hand, the second group uses a consumer-based approach that only partly used lab data., and thus does not allow for a direct comparison between the studies of both groups. The recommendation from the second group to always use the ‘eco’ programmes for normally soiled dishes, may not resonate with the majority of consumers, as most are unwilling to accept the long duration of these programmes or fear potential negative effects associated with long-running times. However, Bichler et al. ¹⁴ found that consumer acceptance of ’eco’ programmes is high when people understand its purpose and are confident that it saves energy and water while maintaining cleaning and drying performance. Another challenge with normally soiled dishes is that no household has only one type of soil, they typically have a mix of lightly, moderately and heavily soiled items. Of course, with different degrees of soiling of the load, the most intensive soiling defines the soiling category of the programme to be selected.

When translating these scientific results into recommendations, combining a lab-based approach with a consumer-based approach might pose a challenge. Moreover, it is essential to ensure that these recommendations can be easily integrated into consumers’ daily routines and do not lead to significant failures or disappointments. Such outcomes may potentially lead to the adoption of compensatory behaviours among consumers, including:

1. The use of alternative programmes or modifiers (which are likely to consume more energy and water).

2. Additional manual pre-washing of dishes before placing them in the dishwasher, or cleaning the dishes manually (which increases water usage, and may also increase energy and detergent consumption).

3. Increased dosing of detergent (which increases detergent use and environmental burden).

The presence of compensatory behaviours has been demonstrated not only in consumer behaviour surveys ^{14 , 15 , 22} but also in controlled, blinded consumer tests using laundry detergent. ²³ These tests revealed a statistically significant increase in wash temperature and detergent use as consumers compensated for a poorer (than expected) cleaning performance. Of course, the impact of compensatory behaviours depends on the proportion of consumers who adopt them. Overall recommendations could still have a positive impact on the sustainability of dishwashing if only a small proportion of consumers engage in compensatory behaviours.

In summary, recommendations should focus on promoting environmentally friendly and resource-efficent solutions while ensuring high consumer satisfaction.

4 Possible consensus

When revisiting the Sinners’ Circle as it applies to the ‘eco’ programme (Figure 2B) it is imporant to note that the chemistry factor is defined using reference detergent type D, according to the European standard EN 60436, titled ‘Electric dishwashers for household use – Methods for measuring the performance’. This standard defines both the composition and quantity of the detergent to be used in tests, ensuring that data is collected under consistent conditions. This consistency is crucial for allowing market surveillance authorities to reproduce the reported values for dishwashers. While the reference detergent used is updated regularly (the next update is planned for 2025, when type D will be replaced by a better-performing reference detergent type E), it does not match the actual detergents available on the market.

Figure 2:

Sinner’s circle showing how a decreased temperature can be compensated either by time (B) in a ’eco’ programme or by chemistry (C) in a ‘short eco’ programme (source: modified according to 1]).

As Tewes et al. have shown, there are significant differences in the performance of detergents currently available in the market. ^{17 , 19} Consequently, when consumers use high-performing detergents, they are likely to achieve better cleaning results than the reference detergent, even in programmes that do not perform as well as ‘eco’ programmes. On the other hand, the performance of high- and low-performing detergents has shown similar effectiveness in the eco programme, ¹⁶ which may result in an “overachievement” in terms of performance.

This insight suggests that Sinners’ circle could be re-evaluated. Specifically, it indicates that either time or chemistry can compensate for the reduction in temperature (Figure 2C). In the context of the Sinners’ Circle, this means that a programme using a high-performing detergent, while maintaining the same ‘mechanics’, can consume the same amount of energy as the ‘eco’ programme but achieve similar cleaning results in a considerably shorter duration.

To implement this approach, it is essential that consumers can easily identify which detergents qualify as high-performing and which dishwasher programmes can deliver effective cleaning with low energy use in the shortest possible time. Therefore, it is crucial to establish a unique name and symbol for this ‘short eco’ programme on dishwashers, as well as a performance indication on the detergent packaging. Regarding the dishwasher, the term ‘eco’ is regulated by the Ecodesign Regulation (EU) 2019/2022, which states in Annex II, Section 1b that “the name ‘eco’ shall be used exclusively for this programme. The only other additional information which may be combined with the term ‘eco’ is the temperature of the eco programme”. As a result, using a name like ‘short eco’ for this new resource-saving programme could encounter legal issues. An alternative name and symbol should be developed for use by detergent manufacturers on suitable detergent packs, as well as by dishwashing manufacturers to identify this type of programme. Some have suggested honouring Herbert Sinner, the creator of the Sinner Circle, by naming this cycle the ‘Sinner Cycle’ and using the Sinner Circle as an iconographic logo for both qualifying detergents and the ‘short eco’ programme symbol.

This requires effective co-operation between the detergent industry and dishwasher manufacturers, as it only makes sense if both detergents and dishwashers convey the same message. This type of co-operation has often failed in the past because of differences in the innovation cycles of detergents and dishwashers. However, in the case of the ‘short eco’ cycle, this may be less restrictive as there are already high-performing detergents available on the market and there may be programmes on existing dishwashing machines which would qualify as ‘short eco’ cycles. If this is the case, manufacturers simply need to inform customers that their respective products are suitable for this purpose. It may even be possible to update the programme names and/or structures of installed dishwashers by leveraging the connectivity features that many modern dishwashers possess.

To achieve this, there are some major open questions:

1. How to organise the collaboration between detergent industry and machine industry?

Compliance laws require that the proposed co-operation between industries adheres to antitrust regulations to prevent anti-competitive practices and price control. Therefore, the collaboration must be open to everyone who wants to participate and thus should be organised within (or with the help of) existing industry associations such as A.I.S.E. or APPLiA.

1. How to define quality criteria for ‘suitable’ detergents and programmes?

For a ‘short eco’ programme, these quality criteria could be formulated as follows:

1. The cleaning performance, measured according to the latest EN 60436 with any qualified high-performance detergent, should match the performance required by the Ecodesign Regulation for the ‘eco’ programme in the same dishwasher.

2. The drying performance, measured according to the latest EN 60436 with any high-performance detergent, should meet the requirements set by the Ecodesign Regulation for the ‘eco’ programme in the same dishwasher.

3. The energy use should be comparable to that required for the ‘eco’ programme in that dishwasher according to the Ecodesign Regulation.

4. The programme duration should be as short as possible while still achieving the required performance.

5. The water use should comply with the Ecodesign Regulation for the ‘eco’ programme in the same dishwasher.

1. For a high-performing detergent, quality criteria could be formulated as follows:

   1. The cleaning performance is X % better in an IKW-test ²⁴ using the programme P4 in the GSL-3 reference dishwasher as average of all soil classes compared to IEC detergent type E (IEC 60436, 4th edition) using the recommended dosage (X to be determined after initial testing).

   2. The drying performance is equal to or better in a test following IEC 60436, 4th edition, Annex Q) using the programme P4 in the GSL-3 reference dishwasher compared to a test with the IEC detergent type E, rinse-aid type III (IEC 60436, 4th edition) using the recommended dosage or using equivalent test procedures of soiling and spotting on dishes.

1. Compliance and verification procedure

5 Way forward

There are several additional points that need to be clarified as we work towards implementing the proposal outlined above. First, the recommendation to combine a high-performing detergent with a compatible ‘short eco’ programme should be analysed for its optimal environmental impact. While it has been shown that the use phase – particularly the temperature used in the cycle – has the greatest impact on the carbon footprint of dishwashing, ²⁵ a comprehensive life cycle assessment should be conducted to ensure that the use of a ‘short eco’ program with a qualified detergent does not significantly worsen environmental outcomes.

Since the proposed approach depends on the voluntary participation of partners from both the detergent and dishwasher industries, their interest, acceptance, and willingness to engage are of the utmost importance. With this in mind, this paper aims to initiate a broad discussion among these partners and other stakeholders to ensure we fully understand the problem and gather insights on potential to the concept and its implementation. All stakeholders – environmental scientists, consumer representatives, policy makers, test institutes, etc. – are encouraged to share their opinions or concerns regarding the proposed approach.

We highly appreciate your feedback (to the corresponding author), which will be treated strictly confidentially. Topics for discussion may include, but are not restricted to:

1. Is this approach clearly described and sufficiently appealing?

2. What additional hurdles and critical factors should be considered?

3. Are the drafted quality criteria adequate? If not, how can they be improved?

4. Is a relevant impact of compensatory behaviours (see above) for sustainability of dishwashing to be expected?

5. How can we effectively communicate the relationship between a ‘short eco’ programme and a suitable detergent (in terms of naming, icons, etc.)?